1. Field of the Invention
The invention relates to a process for producing a liquid crystal cell, or more precisely, a process for treating an organic orientation layer on a substrate plate for a liquid crystal cell.
2. Description of the Prior Art
Orientation layers of the type mentioned above serve to generate an orientation and a pretilt of the liquid crystal molecules. The term `orientation` is here taken to mean the angle between the edge of a substrate plate and the projection of a liquid crystal molecule onto this substrate plate. The pretilt is the angle by which a liquid crystal molecule is tilted against the plane of the substrate plate.
Orientation layers of the type mentioned are produced with two different material groups using two different processes. One process utilizes inorganic materials which are vacuum-deposited slantwise onto the substrate plate in the direction of orientation. The second process utilizes organic substances which, for example, are applied by spraying, immersion or (as a rule) by spincoating. The polymer films are subjected to a tempering process, and then rubbed with a soft material (generally velvet) affixed to a roller. This rubbing is performed in the desired direction of orientation.
It is known from DE 27 22 389 Al, which corresponds to U. S. Pat. No. 4,207,671, which is incorporated herein by reference, that for orientation and pretilt setting both processes are used jointly, i.e., both slantwise deposition and rubbing. The rubbing is performed several times in a specified direction. The direction specified will, when a steep deposition angle has been used, stand at right angles to the projection of the deposition direction onto the substrate plate. In the case of flat deposition angles, rubbing is performed parallel to the projection of the deposition direction onto the substrate plate, from the side on which due to the slantwise deposition the liquid crystal molecules lie deeper in the finished liquid crystal cell, i.e., in the direction of rising pretilt, so to speak. This process permits the pretilt (which is also relatively steep with flat slantwise deposition) to be set to smaller values.
While when using slantwise-deposited inorganic orientation layers there tend to be problems with the finished liquid crystal cells due to excessively high pretilt angles, the situation is rather the opposite when polymer rubbed orientation layers are used. Efforts have been made in this context to achieve higher pretilt angles by developing the materials used. Attempts have also been made not to rub the materials, but instead to cause an orientation of the polymer orientation-layer molecules by pouring these on in the orientation direction or by means of other flowapplication processes. It seemed desirable to avoid the rubbing, since it was known that rubbing reduces the originally-attainable high pretilt angles (see in this context the findings of U.S. Pat. No. 4,207,671 cited above).
All attempts so far made to develop better materials for orientation layers and to improve production methods for such layers have not yet led to fully satisfactory results, i.e., to polymer orientation layers with which very high pretilt angles can be simply and reliably achieved.